Production method of optical film

ABSTRACT

The present application relates to an optical film and a method for producing a polarizing plate. The present application can provide an optical film satisfying optical and mechanical durability required in a polarizing plate effectively and capable of forming a polarizing plate without causing bending when applied to a display device, and a method for producing a polarizing plate to which the optical film is applied. The present application can provide an optical film capable of realizing the required optical and mechanical durability without causing bending even in a polarizing plate applied to a thin display device and/or a thin polarizing plate, and a method for producing a polarizing plate to which the optical film is applied.

TECHNICAL FIELD

This application claims priority based on Korean Patent Application No.10-2019-0003684 filed on Jan. 11, 2019, the disclosure of which isincorporated herein by reference in its entirety.

The present application relates to a method for producing an opticalfilm or a polarizing plate.

BACKGROUND ART

Polarizing plates are optical films applied to control light states invarious display devices. Usually, the polarizing plate is produced byattaching a protective film to one side or both sides of a polarizingfilm with a polarizing function.

Since the polarizing plate is exposed to various temperature andhumidity conditions depending on the use environment of the displaydevice, it requires durability. For example, the polarizing plate shouldstably maintain the designed optical properties according to theexternal environment such as temperature and humidity, and should notcause mechanical defects such as cracks.

The protective film of the polarizing film should be selected so thatthe polarizing plate can satisfy the required physical properties asabove.

Recently, as the demand for thinner display devices increases, there isalso a demand for thin polarizing plates that do not cause bending.Since the polarizing film or other components included in the polarizingplate are usually produced through a stretching process, they tend togenerate stress depending on external temperature and humidity. Suchstress can cause bending in thin display devices, and such bending canadversely affect the performance of the display devices.

DISCLOSURE Technical Problem

The present application relates to an optical film and a method forproducing a polarizing plate. It is an object of the present applicationto provide an optical film effectively satisfying optical and mechanicaldurability required in the polarizing plate and capable of forming apolarizing plate without causing bending when applied to a displaydevice, and a method for producing a polarizing plate applying theoptical film.

It is one object of the present application to provide an optical filmcapable of realizing the required optical and mechanical durabilitywithout causing bending even in a polarizing plate applied in a thindisplay device and/or a polarizing plate having a thin thickness and amethod for producing a polarizing plate applying the optical film.

Technical Solution

In this specification, the term such as vertical, horizontal, orthogonalor parallel among terms defining an angle means substantially vertical,horizontal, orthogonal or parallel in the range without impairingintended effects, and the range of vertical, horizontal, orthogonal orparallel includes an error such as a production error or a deviation(variation). For example, each case of the foregoing may include anerror within about ±15 degrees, an error within about ±10 degrees or anerror within about ±5 degrees.

Among physical properties referred to herein, when the measuredtemperature affects relevant physical properties, the physicalproperties are physical properties measured at room temperature, unlessotherwise specified.

In this specification, the term room temperature is a temperature in astate without particularly warming or cooling, which may mean onetemperature in a range of about 10° C. to 30° C., for example, atemperature of about 15° C. or higher, 18° C. or higher, 20° C. orhigher, or about 23° C. or higher, and about 27° C. or lower. Unlessotherwise specified, the unit of the temperature mentioned herein is °C.

Among physical properties referred to herein, when the measured pressureaffects relevant physical properties, the physical properties arephysical properties measured at normal pressure, unless otherwisespecified. In this specification, the term normal pressure is a naturalpressure without particularly pressurizing or depressurizing, whichusually means a pressure of about 1 atm or so, such as atmosphericpressure.

Among physical properties referred to herein, when the measured humidityaffects relevant physical properties, the physical properties arephysical properties measured at any one humidity in a range of about 0RH % to 100 RH %, for example, relative humidity of about 90 RH % orless, about 80 RH % or less, about 70 RH % or less, about 60 RH % orless, about 50 RH % or less, about 40 RH % or less, about 30 RH % orless, about 20 RH % or less, about 18 RH % or less, about 15 RH % orless, or about 10 RH % or less, or about 1 RH % or more, about 2 RH % ormore, about 5 RH % or more, about 10 RH % or more, about 15 RH % ormore, about 20 RH % or more, about 25 RH % or more, about 30 RH % ormore, about 35 RH % or more, about 40 RH % or more, or about 45 RH % ormore, unless otherwise specified. Here, the unit RH % means that therelevant humidity is the relative humidity (unit: %).

Unless otherwise specified, the angle formed by any two directions,which is mentioned herein, may be an acute angle of acute angles toobtuse angles formed by the two directions, or may be a small angle fromangles measured in clockwise and counterclockwise directions. Thus,unless otherwise specified, the angles mentioned herein are positive.However, in order to display the measurement direction between theangles measured in the clockwise direction or the counterclockwisedirection if necessary, the angle measured in the clockwise directionmay be represented as a positive number, and the angle measured in thecounterclockwise direction may be represented as a negative number.

The method for producing an optical film of the present application maycomprise a step of heat-treating a polymer film having an optical layerformed on its surface.

The optical film produced in the method of the present application maybe a film that exhibits one or more optically intended functions, andmay be, for example, a protective film of a polarizing film.

In the present application, it has been confirmed that a polymer film isheat-treated in a state where an optical layer is formed on its surface,whereby the secured properties of the polymer film greatly contribute toproducing the desired polarizing plate. Such heat-treatment isparticularly effective for polymer films having mechanical anisotropy,as described below. The optical layer may be formed only on one surfaceof the polymer film. That is, the heat-treatment of the polymer film maybe performed in a state where the optical layer is formed asymmetricallyon the polymer film.

Here, the kind of the optical layer formed on the surface of the polymerfilm is not particularly limited. The optical layer may be, for example,a layer comprising a so-called hard coating layer, an antireflectionlayer or an antiglare layer, or an antistatic layer, and the like, ormay be an optical layer that two or more functions are compounded amongthe functions represented by the above-mentioned layers.

The hard coat layer is usually formed for the purpose of preventingscratches on the surface of the polarizing plate or the optical film.The antireflection layer is usually performed for the purpose ofpreventing the reflection of external light on the surface of thepolarizing plate or the optical film, and the antiglare layer is a layerformed for the purpose of preventing visibility from deteriorating dueto external light reflection on the surface of the polarizing plate orthe optical film. In addition, the antistatic layer is usually a layerformed to prevent the phenomenon that the optical film is unnecessary orexcessively charged by adjusting the electrical resistance of theoptical film to an appropriate level.

The material of the above-mentioned optical layer and a method offorming the same are well known in the industry of optical films such aspolarizing plates, and such known materials and methods may be appliedin the present application.

Typically, the above-mentioned optical layers comprise a photocurablebinder, and thus the optical layers applied in the present applicationalso comprise a photocurable binder. Here, the photocurable binder meansa binder formed by curing or polymerizing a photocurable orphotopolymerizable compound. Here, in the category of light that inducescuring or polymerization of the photocurable or photopolymerizablecompound, particle beams such as alpha-particle beams, proton beams,neutron beams or electron beams, and the like, as well as microwaves,infrared rays (IR), ultraviolet rays (UV), X-rays and gamma rays, mayalso be included. Usually, an ultraviolet-ray or electron-beam curing orpolymerizable compound is used as the binder of the optical layer.

As typical photocurable or photopolymerizable compounds, acryliccompounds may be exemplified.

For example, the optical layer may be formed by coating a coatingcomposition containing the acrylic compound as the binder andcrosslinking or polymerizing the compound. Therefore, the optical layermay be a crosslinked layer or a cured layer of the curable compositioncomprising a crosslinked product or a cured product of the acryliccompound as the binder.

A non-limiting example of the applicable acrylic compound includes a(meth)acrylic acid diester such as neopentyl glycol diacrylate,1,6-hexanediol di(meth)acrylate or propylene glycol di(meth)acrylate; a(meth)acrylic acid diester of a polyoxyalkylene glycol such astriethylene glycol di(meth)acrylate, dipropylene glycoldi(meth)acrylate, polyethylene glycol di(meth)acrylate or polypropyleneglycol di(meth) acrylate; a (meth)acrylic acid diester of a polyhydricalcohol such as pentaerythritol di(meth)acrylate; a compound such asepoxy (meth)acrylate, urethane (meth)acrylate or polyester(meth)acrylate, or a multifunctional compound having 3 or more(meth)acryloyl groups such as trimethylolpropane tri(meth)acrylate,trimethylolethane tri(meth)acrylate, 1,2,4-cyclohexanetetra(meth)acrylate, pentaglycerol triacrylate, pentaerythritoltetra(meth)acrylate, pentaerythritol tri(meth)acrylate,(di)pentaerythritol triacrylate, (di)pentaerythritol pentaacrylate,(di)pentaerythritol tetra(meth)acrylate, (di)pentaerythritolhexa(meth)acrylate, tripentaerythritol triacrylate or tripentaerythritolhexatriacrylate, and the like.

The optical layer or the curable composition for forming the opticallayer may further comprise any additive for securing a necessaryfunction in addition to the binder. For example, the optical layer orthe curable composition may comprise an initiator or a catalyst forinitiating or accelerating curing or crosslinking of the acryliccompound, high refractive or low refractive particles for controllingthe refractive index of the relevant optical layer, or any additive suchas a surfactant or a leveling agents, and the kind thereof is notparticularly limited.

The method for producing the optical film may comprise a step ofsteam-treating the polymer film before the heat-treatment; and a step offorming the optical layer on the surface of the steam-treated polymerfilm.

The steam treatment step is a step of exposing the polymer film tosteam, where the flatness of the polymer film can be improved by thisstep. After the optical layer is formed on the surface of the polymerfilm having improved flatness, the above-described heat-treatment may beperformed to more effectively secure the desired characteristics.

The manner of performing the steam treatment is not particularlylimited. For example, it may be performed in a manner of positioning thepolymer film on a flat surface, positioning the polymer film in thedirection parallel to the gravity direction, or positioning the polymerfilm at another position where the flatness may be secured and thenexposing all or part of the polymer film to steam.

The steam treatment may be performed by applying steam having anappropriate range of temperature as the steam applied to the treatmentin consideration of the glass transition temperature of the polymerfilm. In one example, the temperature of the steam applied at the timeof the steam treatment may be in a range of 50° C. to 150° C. In anotherexample, the steam temperature may be about 55° C. or higher, about 60°C. or higher, about 65° C. or higher, about 70° C. or higher, about 75°C. or higher, or about 80° C. or higher, or may also be about 145° C. orlower, about 140° C. or lower, about 135° C. or lower, about 130° C. orlower, about 125° C. or lower, about 120° C. or lower, about 115° C. orlower, about 110° C. or lower, about 105° C. or lower, or about 100° C.or lower.

The time for performing the steam treatment may be set within a range inwhich the desired flatness of the polymer film may be secured, and thespecific range may be changed by the state of the polymer film, thetemperature of steam, and the like. Typically, the steam treatment maybe performed for 10 seconds to 1 hour. In another example, the steamtreatment time may be about 55 minutes or less, about 50 minutes orless, about 45 minutes or less, about 40 minutes or less, about 35minutes or less, about 30 minutes or less, about 25 minutes or less,about 20 minutes or less, about 15 minutes or less, about 10 minutes orless, about 5 minutes or less, or about 1 minute or less, or may also beabout 20 seconds or more or so.

The manner of forming the optical layer after the steam treatment is notparticularly limited, where the optical layer may be formed according toa known manner of forming the optical layer. For example, the opticallayer may be formed in a manner of coating a curable compositionprepared by using the acrylic compound as the above-described binder andother necessary additives on one side of the polymer film, and thencrosslinking or polymerizing the acrylic compound.

The polymer film in which the heat-treatment is performed may be a filmhaving a mechanically specific asymmetry property. By applying such afilm to the heat-treatment process, the object can be effectivelyachieved.

The physical properties of the polymer film referred to herein are eachmeasured according to the methods described in the example section ofthis specification.

The term first direction and second direction of the polymer film usedin this specification is any in-plane direction of the polymer film. Forexample, when the polymer film is a stretched polymer film, the in-planedirection may be an in-plane direction formed by MD (machine direction)and TD (transverse direction) directions of the polymer film. In anotherexample, the first direction may be any one of MD (machine direction)and TD (transverse direction) directions when the polymer film is astretched polymer film, and the second direction may be the other of MD(machine direction) and TD (transverse direction) directions.

In one example, the first direction of the polymer film referred toherein may be the TD direction.

The asymmetry property of the polymer film may be represented byshrinkage force of the polymer film. The shrinkage force (shrinkageforce of optical film, polymer film, polarizing film or polarizingplate) referred to herein is measured in the manner described in thefollowing examples. In addition, the shrinkage force may be measured ina state of the polymer film alone or where the optical layer is formedon the polymer film.

In one example, the polymer film may have shrinkage force in the firstdirection (for example, the above-described TD direction) before theheat-treatment in a range of 5.5N to 15N. In another example, theshrinkage force of the polymer film in the first direction may be about6N or more, about 6.5 N or more, about 7 N or more, or about 7.5 N ormore, or may be about 15 N or less, 14 N or less, 13 N or less, 12 N orless, 11 N or less, 10 N or less, 9 N or less, or 8 N or less. This highshrinkage force in one direction allows the desired optical film to beeffectively formed after the heat-treatment process.

In the polymer film, a ratio (S1/S2) of shrinkage force (S1) in thefirst direction and shrinkage force (S2) in an in-plane second directionperpendicular to the first direction before heat-treatment may be 10 ormore. In another example, the ratio (S1/S2) may be about 11 or more,about 12 or more, about 13 or more, about 14 or more, about 15 or more,or about 15.5 or more, or may be about 150 or less, about 140 or less,about 130 or less, about 120 or less, about 110 or less, about 100 orless, about 90 or less, or about 80 or less or so. Here, in one example,the in-plane second direction may be the MD direction.

The polymer film may have shrinkage force in the second direction (forexample, the above-described MD direction) in a range of 0.01N to 2Nbefore the heat-treatment. In another example, the shrinkage force ofthe polymer film in the second direction may be about 0.03N or more,about 0.05N or more, about 0.07 N or more, or about 0.09 N or more, ormay be about 1.8 N or less, 1.6 N or less, 1.4 N or less, 1.2 N or less,1 N or less, 0.8 N or less, or 0.6 N or less or so. This high shrinkageforce in one direction allows the desired optical film to be effectivelyformed after the heat-treatment process.

As the polymer film having relatively high shrinkage force and/or anasymmetry property of shrinkage force as above, a film known as aso-called high-stretched PET (poly(ethylene terephthalate)) film or SRF(super retardation film) exhibiting a high phase difference ofapproximately 3,000 nm or more, and the like, is representatively known.Therefore, in the present application, the polymer film may be, forexample, a polyester polymer film. Such a film itself is known in theindustry, and this film exhibits a large asymmetry property ofmechanical physical properties by high stretching or the like during theproduction process. A representative example of the polymer film in astate known in the industry is a polyester film such as a PET(poly(ethylene terephthalate)) film, and for example, there is a film ofthe trade name SRF (super retardation film) series supplied by Toyobo.

Usually, the stretched PET film is a uniaxially stretched film with oneor more layers produced by melting/extruding a PET-based resin to form afilm and stretching it or a biaxially stretched film with one or morelayers produced by longitudinal and transverse stretching it after filmformation.

The PET-based resin generally means a resin in which 80 mol % or more ofrepeating units become ethylene terephthalate, which may also compriseother dicarboxylic acid components and diol components. The otherdicarboxylic acid component is not particularly limited, but it mayinclude, for example, isophthalic acid, p-beta-oxyethoxy benzoic acid,4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone,bis(4-carboxyphenyl)ethane, adipic acid, sebacic acid and/or1,4-dicarboxycyclohexane, and the like.

The other diol component is not particularly limited, but it may includepropylene glycol, butanediol, neopentyl glycol, diethylene glycol,cyclohexanediol, an ethylene oxide adduct of bisphenol A, polyethyleneglycol, polypropylene glycol and/or polytetramethylene glycol, and thelike.

The dicarboxylic acid component or the diol component may be used incombination of two or more as needed. Also, it may be used incombination with an oxycarboxylic acid such as p-oxybenzoic acid. Inaddition, as the other copolymerization component, a diol component, ora dicarboxylic acid component containing a small amount of amide bonds,urethane bonds, ether bonds, carbonate bonds, or the like may also beused.

As a method for preparing a PET-based resin, a method of directlypolycondensing terephthalic acid, ethylene glycol and/or otherdicarboxylic acids or other diols as necessary, a method oftransesterifying a dialkyl ester of terephthalic acid and ethyleneglycol and/or other dialkyl esters of dicarboxylic acids or other diolsas necessary, followed by polycondensation, a method of polycondensingterephthalic acid and/or other ethylene glycol esters of dicarboxylicacids as necessary and/or other diol esters as necessary, and the likeare adopted.

For each polymerization reaction, a polymerization catalyst comprisingan antimony-based, titanium-based, germanium-based or aluminum-basedcompound, or a polymerization catalyst comprising a composite compoundthereof can be used.

The polymerization reaction conditions may be appropriately selecteddepending on the monomers used, the catalyst, the reaction apparatus,and the desired resin physical properties, which are not particularlylimited, but for example, the reaction temperature is usually about 150°C. to about 300° C., about 200° C. to about 300° C. or about 260° C. toabout 300° C. In addition, the reaction pressure is usually fromatmospheric pressure to about 2.7 Pa, where the pressure may be reducedin the latter half of the reaction.

The polymerization reaction proceeds by volatilizing leaving reactantssuch as a diol, an alkyl compound or water.

The polymerization apparatus may also be one which is completed by onereaction tank or connects a plurality of reaction tanks. In this case,the reactants are polymerized while being transferred between thereaction tanks, depending on the degree of polymerization. In addition,a method, in which a horizontal reaction apparatus is provided in thelatter half of the polymerization and the reactants are volatilizedwhile heating/kneading, may also be adopted.

After completion of the polymerization, the resin is discharged from thereaction tank or the horizontal reaction apparatus in a molten state,and then, obtained in the form of flakes cooled and pulverized in acooling drum or a cooling belt, or in the form of pellets tailored afterbeing introduced into an extruder and extruded in a string shape.Furthermore, solid-phase polymerization may be performed as needed,thereby improving the molecular weight or decreasing the low molecularweight component. As the low molecular weight component that may becontained in the PET-based resin, a cyclic trimer component may beexemplified, but the content of such a cyclic trimer component in theresin is usually controlled to 5,000 ppm or less, or 3,000 ppm or less.

The molecular weight of the PET-based resin is usually in a range of0.45 to 1.0 dL/g, 0.50 to 1.0 dL/g or 0.52 to 0.80 dL/g, when the resinhas been dissolved in a mixed solvent of phenol/tetrachloroethane=50/50(weight ratio) and it has been represented as a limiting viscositymeasured at 30° C.

The PET-based resin may contain additives as required. The additive mayinclude a lubricant, an anti-blocking agent, a heat stabilizer, anantioxidant, an antistatic agent, a light stabilizer and an impactresistance improver, and the like. The addition amount thereof ispreferably within a range that does not adversely affect the opticalproperties.

The PET-based resin is used in the form of pellets assembled by anordinary extruder, for formulation of such additives and film molding tobe described below. The size and shape of the pellets are notparticularly limited, but they are generally a cylindrical, spherical orflat spherical shape having both height and diameter of 5 mm or less.The PET-based resin thus obtained can be molded into a film form andsubjected to a stretching treatment to obtain a transparent andhomogeneous PET film having high mechanical strength. The productionmethod thereof is not particularly limited, and for example, thefollowing method is adopted.

Pellets made of the dried PET resin are supplied to a melt extrusionapparatus, heated to a melting point or higher and melted. Next, themelted resin is extruded from the die and quenched and solidified on arotary cooling drum to a temperature below the glass transitiontemperature to obtain an un-stretched film in a substantially amorphousstate. This melting temperature is determined according to the meltingpoint of the PET-based resin to be used or the extruder, which is notparticularly limited, but is usually 250° C. to 350° C. In order toimprove planarity of the film, it is also preferred to enhance adhesionbetween the film and the rotary cooling drum, and an adhesion method byelectrostatic application or an adhesion method by liquid coating ispreferably adopted. The adhesion method by electrostatic application isusually a method in which linear electrodes are provided on the uppersurface side of a film in a direction perpendicular to the flow of thefilm and a direct current voltage of about 5 to 10 kV is applied to theelectrodes to provide static charges to the film, thereby improving theadhesion between the rotary cooling drum and the film. In addition, theadhesion method by liquid coating is a method for improving the adhesionbetween the rotary cooling drum and the film by uniformly coating aliquid to all or a part (for example, only the portion in contact withboth film ends) of the surface of the rotary cooling drum. Both of themmay also be used in combination if necessary. The PET-based resin to beused may be mixed with two or more resins, or resins having differentstructures or compositions, if necessary. For example, it may includeusing a mixture of pellets blended with a particulate filling materialas an anti-blocking agent, an ultraviolet absorbing agent or anantistatic agent, and the like, and non-blended pellets, and the like.

The laminating number of films to be extruded may also be two or morelayers, if necessary. For example, it may include that pellets blendedwith a particulate filling material as an anti-blocking agent andnon-blended pellets are prepared and supplied from the other extruder tothe same die to extrude a film composed of two kinds and three layers,“blended with filling material/non-blended/blended with fillingmaterial,” and the like.

The un-stretched film is usually stretched longitudinally at atemperature not lower than the glass transition temperature in theextrusion direction first. The stretching temperature is usually 70° C.to 150° C., 80 to 130° C., or 90 to 120° C. In addition, the stretchingratio is usually 1.1 to 6 times or 2 to 5.5 times. The stretching may beterminated once or divided into more than once as necessary.

The longitudinally stretched film thus obtained may be subjected to aheat-treatment thereafter. Then, a relaxation treatment may be performedif necessary. The heat-treatment temperature is usually 150° C. to 250°C., 180 to 245° C. or 200 to 230° C. Also, the heat-treatment time isusually 1 to 600 seconds or 1 to 300 seconds or 1 to 60 seconds.

The temperature of the relaxation treatment is usually 90 to 200° C. or120 to 180° C. Also, the amount of relaxation is usually 0.1 to 20% or 2to 5%. The relaxation treatment temperature and the relaxation amountcan be set so that a heat shrinkage rate of the PET film afterrelaxation treatment at 150° C. is 2% or less.

In the case of obtaining uniaxially stretched and biaxially stretchedfilms, transverse stretching is usually performed by a tenter after thelongitudinal stretching treatment or after the heat-treatment orrelaxation treatment, if necessary. The stretching temperature isusually 70° C. to 150° C., 80° C. to 130° C., or 90° C. to 120° C. Inaddition, the stretching ratio is usually 1.1 to 6 times or 2 to 5.5times. Thereafter, the heat-treatment and, if necessary, the relaxationtreatment can be performed. The heat-treatment temperature is usually150° C. to 250° C. or 180° C. to 245° C. or 200 to 230° C. Theheat-treatment time is usually 1 to 600 seconds, 1 to 300 seconds, or 1to 60 seconds.

The temperature of the relaxation treatment is usually 100 to 230° C.,110 to 210° C. or 120 to 180° C. Also, the relaxation amount is usually0.1 to 20%, 1 to 10%, or 2 to 5%. The relaxation treatment temperatureand the relaxation amount can be set so that the heat shrinkage rate ofthe PET film after the relaxation treatment at 150° C. is 2% or less.

In uniaxial stretching and biaxial stretching treatments, in order toalleviate deformation of the orientation main axis as represented bybowing, the heat-treatment can be performed again or the stretchingtreatment can be performed after the transverse stretching. The maximumvalue of deformation in the orientation main axis by bowing with respectto the stretching direction is usually within 45 degrees, within 30degrees, or within 15 degrees. Here, the stretching direction alsorefers to a stretching large direction in longitudinal stretching ortransverse stretching.

In the biaxial stretching of the PET film, the transverse stretchingratio is usually slightly larger than the longitudinal stretching ratio,where the stretching direction refers to a direction perpendicular tothe long direction of the film. Also, the uniaxial stretching is usuallystretched in the transverse direction as described above, where thestretching direction equally refers to a direction perpendicular to thelong direction.

The orientation main axis refers to a molecular orientation direction atany point on the stretched PET film. Furthermore, the deformation of theorientation main axis with respect to the stretching direction refers toan angle difference between the orientation main axis and the stretchingdirection. In addition, the maximum value thereof refers to a maximumvalue of the values on the vertical direction with respect to the longdirection. The method of identifying the orientation main axis is known,and for example, it can be measured using a retardation film/opticalmaterial inspection apparatus RETS (manufactured by Otsuka Densi KK) ora molecular orientation system MOA (manufactured by Oji ScientificInstruments).

The thickness of the polymer film applied in the present application isdetermined depending on the use, which is not particularly limited. Forexample, the thickness of the polymer film may be in a range of about 20μm to 250 μm. In another example, the thickness may be about 240 μm orless, about 230 μm or less, about 220 μm or less, about 210 μm or less,about 200 μm or less, about 190 μm or less, about 180 μm or less, about170 μm or less, about 160 μm or less, 150 μm or less, about 140 μm orless, about 130 μm or less, about 120 μm or less, about 110 μm or less,or 100 μm or less, or may be about 30 μm or more, 40 μm or more, 50 μmor more, 60 μm or more, or 70 μm or more or so.

The heat-treatment of the polymer film may be performed such that theratio (SB/SA) of the shrinkage force (SB) of the polymer film before theheat-treatment in the first direction and the shrinkage force (SA) ofthe polymer film after the heat-treatment may exceed approximately 1. Inanother example, the ratio (SB/SA) may be about 1.01 or more, about 1.02or more, about 1.03 or more, 1.04 or more, about 1.05 or more, about1.06 or more, about 1.07 or more, about 1.08 or more, about 1.09 ormore, about 1.1 or more, about 1.11 or more, about 1.12 or more, about1.13 or more, 1.14 or more, about 1.15 or more, about 1.16 or more,about 1.17 or more, about 1.18 or more, about 1.19 or more, about 1.2 ormore, about 1.21 or more, about 1.22 or more, or about 1.23 or more, ormay also be about 10 or less, about 9 or less, about 8 or less, about 7or less, about 6 or less, about 5 or less, about 4 or less, about 3 orless, about 2 or less, about 1.9 or less, about 1.8 or less, about 1.7or less, about 1.6 or less, about 1.5 or less, about 1.4 or less, orabout 1.3 or less or so. The overall physical properties of the polymerfilm may be maintained at a desired level by the heat-treatmentperformed so that the shrinkage force of the polymer film in the firstdirection is corrected within the range.

The polymer film may have shrinkage force in the first direction afterheat-treatment within a range of approximately 5 to 10N. In anotherexample, the shrinkage force in the first direction after theheat-treatment may be about 5.1N or more, about 5.2N or more, about 5.3Nor more, about 5.4N or more, about 5.5N or more, 5.6N or more, 5.7N ormore, 5.8N or more, 5.9N or more, 6N or more, 6.1N or more, 6.2N ormore, 6.3N or more, 6.4N or more, 6.5N or more, 6.6N or more, 6.7N ormore, 6.8N or more, 6.9N or more, about 7N or more, or about 7.1 ormore, or may be about 9.5N or less, about 9N or less, about 8.5N orless, about 8 or less, about 7.5N or less, 7.3N or less, 7.2N or less,7.1N or less, 7.0N or less, or 6.9N or less. The overall physicalproperties of the polymer film may be maintained at a desired level bythe heat-treatment performed so that the shrinkage force of the polymerfilm in the first direction is corrected within the range.

The polymer film may have a ratio (S1/S2) of the shrinkage force (S1) inthe first direction (for example, the TD direction) and the shrinkageforce (S2) in the in-plane second direction (for example, the MDdirection) perpendicular to the first direction after the heat-treatmentof 13 or more. In another example, the ratio (S1/S2) may be about 14 ormore, about 15 or more, about 16 or more, about 17 or more, or about17.5 or more, or may be about 150 or less, about 140 or less, about 130or less, about 120 or less, about 110 or less, about 100 or less, about90 or less or about 80 or less, about 70 or less, about 60 or less,about 50 or less, about 40 or less, or about 38 or less or so. Theoverall physical properties of the polymer film may be maintained at adesired level by the heat-treatment performed so that the shrinkageforce of the polymer film is corrected within the range.

The polymer film may have shrinkage force in the second direction (forexample, the above-described MD direction) after the heat-treatment in arange of 0.05N to 3N. In another example, the shrinkage force of thepolymer film in the second direction may be about 0.07N or more, about0.09N or more, about 0.1N or more, about 0.15N or more or about 0.2N ormore, or may be about 1.8N or less, 1.6N or less, 1.4 N or less, 1.2 Nor less, 1 N or less, 0.8 N or less, 0.6 N or less, or about 0.4 N orless or so. The overall physical properties of the polymer film may bemaintained at a desired level by heat-treatment performed so that theshrinkage force of the polymer film is corrected within the range.

In general, when the heat-treatment temperature is high or theheat-treatment time is long, the shrinkage force tends to be reduced, sothat the heat-treatment conditions can be appropriately adjusted inconsideration of this.

The above-described high-stretched polyester film exhibits an asymmetryproperty, as described above, but it is not easy to achieve the desiredshrinkage force characteristics in the present application by itself.Therefore, in the present application, a predetermined heat-treatment isperformed on the high-stretched polyester film to adjust thecharacteristics. For example, the shrinkage force of the polymer filmmay be reduced through heat-treatment at a predetermined range oftemperature based on the glass transition temperature (Tg) of therelevant film. For example, when the glass transition temperature of therelevant protective film is set as Tg (unit: ° C.), the heat-treatmentis performed at a temperature within the range of Tg−60 (° C.) to Tg+50(° C.), whereby the shrinkage force or the like can be adjusted to thedesired range. In this case, generally, the shrinkage force iscontrolled in the TD (transverse direction) direction rather than theso-called MD (machine direction) direction.

In another example, the heat-treatment temperature may be Tg+45° C. orless, Tg+40° C. or less, Tg+35° C. or less, Tg+30° C. or less, Tg+25° C.or less, Tg+20° C. or less, Tg+15° C. or less, Tg+10° C. or less, Tg+5°C. or less, Tg° C. or less, Tg−5° C. or less, Tg−10° C. or less, Tg−15°C. or less, Tg−20° C. or less, Tg−25° C. or less, Tg−30° C. or less, orTg−35° C. or less or so, or may be Tg−55° C. or more, Tg−50° C. or more,Tg−45° C. or more, or Tg−40° C. or more, wherein Tg is the glasstransition temperature.

In the present application, it has been confirmed that the desiredcharacteristics can be secured by performing heat-treatment at such atemperature on the highly stretched polyester film. Considering thedesired characteristics, the time for which the heat-treatment isperformed can be adjusted without particular limitation, and it may begenerally performed within the range of about 10 seconds to 1,000seconds. In another example, the heat-treatment time may be about 15seconds or more, about 20 seconds or more, about 25 seconds or more, orabout 30 seconds or more, or may also be about 900 seconds or less,about 850 seconds or less, about 800 seconds or less, about 750 secondsor less, about 700 Seconds or less, about 650 seconds or less, about 600seconds or less, about 550 seconds or less, about 500 seconds or less,about 450 seconds or less, about 400 seconds or less, about 350 secondsor less, about 300 seconds or less, about 250 seconds or less, about 200seconds or less, about 150 seconds or less, about 100 seconds or less,or about 90 seconds or less or so.

The optical film may be formed by correcting the asymmetry property ofthe polymer film to a desired level through the heat-treatment as above.

The present application also relates to a method for producing apolarizing plate using the optical film produced in the same manner asabove.

In this specification, the terms polarizing film and polarizing platehave different meanings. The term polarizing film means a functionalelement itself exhibiting a polarizing function, such as, for example, aPVA (poly(vinyl alcohol))-based film in which an anisotropic substancesuch as iodine is adsorbed and oriented, and the polarizing plate meansan element comprising other elements together with the polarizing film.Here, other elements included together with the polarizing film can beexemplified by a polarizing film protective film, a viewing anglecompensating film, a hard coating layer, a phase difference film, anadhesive layer, a pressure-sensitive adhesive layer, an antistatic layeror a low reflection layer, and the like, but is not limited thereto.

The optical film produced by the method of the present application maybe another element included in the polarizing plate together with thepolarizing film, and in one example, the optical film may be applied asthe protective film of the polarizing film.

The polarizing plate produced in the present application may have atotal thickness of 200 μm or less. That is, the polarizing plate maycomprise various elements as described above, but the final thicknessmay be limited within the range. When the thickness of the polarizingplate is set as 200 μm or less, it can cope effectively with variousapplications for which the thin thickness is required. Usually, on apolarizing plate, a pressure-sensitive adhesive layer for applying thepolarizing plate to a display device is formed, and in order to protectthe pressure-sensitive adhesive layer, optionally, a release film isattached to the pressure-sensitive adhesive layer or a releasesurface-protective sheet is temporarily attached to the outermost sideof the polarizing plate. The thickness of 200 μm or less mentioned inthe present application is a thickness excluding portions finallyremoved when the polarizing plate is applied to a display, such as therelease film or the surface-protective sheet. In another example, thethickness may be about 195 μm or less, about 190 μm or less, about 185μm or less, about 180 μm or less, about 175 μm or less, about 170 μm orless, about 165 μm or less, about 160 μm or less, about 155 μm or less,about 150 μm or less, about 145 μm or less, or about 140 μm or less orso. The lower limit of the thickness of the polarizing plate is notparticularly limited, but it may generally be about 50 μm or more, 60 μmor more, 70 μm or more, 80 μm or more, 90 μm or more, 100 μm or more,110 μm or more, or 120 μm or more or so.

The thickness referred to herein may mean the shortest distance, themaximum distance or the average distance connecting the major surface ofthe target article to the main back, where there may also bemanufacturing errors or deviations of a certain portion.

The polarizing plate may basically comprise a polarizing film and theoptical film, wherein the optical film may be included as the protectivefilm of the polarizing film. In addition, the polarizing plate maycomprise a pressure-sensitive adhesive layer. Such a pressure-sensitiveadhesive layer may be a pressure-sensitive adhesive layer for attachingthe polarizing plate to a display device. When the pressure-sensitiveadhesive layer is included, the components of the polarizing plate maybe arranged in the order of the optical film, the polarizing film, andthe pressure-sensitive adhesive layer.

Therefore, the production method may comprise a step of attaching thepolarizing film and the optical film produced by the method. Inaddition, the production method of the polarizing plate may also furthercomprise a step of forming a pressure-sensitive adhesive layer on thesurface of the side opposite to the surface of the polarizing film towhich the optical film is attached.

The pressure-sensitive adhesive layer may be present for attaching thepolarizing plate to a display device such as an LCD or an OLED. Thepressure-sensitive adhesive for forming the pressure-sensitive adhesivelayer is not particularly limited, and for example, an acrylic polymer,a silicone-based polymer, polyester, polyurethane, polyamide, polyetheror a polymer such as a fluorine series or a rubber series as a basepolymer can be appropriately selected and used. As described above, withrespect to the exposed surface of the pressure-sensitive adhesive layer,a release film may be temporarily attached thereto and covered for thepurpose of preventing the contamination until the layer is provided forpractical use.

The thickness of the pressure-sensitive adhesive layer may usually be ina range of 5 μm to 100 μm. In another example, the thickness may beabout 10 μm or more, 15 μm or more, or 20 μm or more, or may be about 90μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less,40 μm or less, or 30 μm or less.

As the polarizing film, a polarizing film in which a light absorptionaxis is formed along one in-plane direction can be used. Such polarizingfilms are variously known. In one example, as the polarizing film, apoly(vinyl alcohol) (hereinafter, PVA)-based polarizing film, which is atypical linear absorption polarizing film, can be used. Such apolarizing film usually comprises a PVA film and an anisotropicabsorbent material adsorbed and oriented on the PVA film. As theanisotropic absorbent material, various dichroic dyes may be used, andiodine-based materials may be typically used. Such a polarizing film isgenerally referred to as an iodine-based absorbent linear PVA polarizingfilm.

For example, the PVA-based polarizing plate may be produced bysubjecting a PVA-based film to various treatments such as swelling,dyeing, cross-linking and stretching, followed by cleaning and dryingprocesses. As described below, the polarizing film can adjust shrinkageforce to a predetermined range, where the shrinkage force can becontrolled by adjusting the process conditions in any of the processes.In general, the shrinkage force may be influenced by draw ratios or thelike during the stretching process of the processes. That is, when thedraw ratio is high, the shrinkage force may be high, and when the drawratio is low, it may be low. However, this method corresponds to oneexemplary method in which the shrinkage force can be controlled, andthose skilled in the field of manufacturing the polarizing film caneasily produce a polarizing film having a desired shrinkage forceaccording to the purpose.

The polarizing film of the present application is the iodine-baseabsorption linear PVA polarizing film, which may comprise a PVA-basedfilm and an anisotropic absorbent material adsorbed and oriented on thePVA-based film.

As the PVA-based film, for example, a general PVA-based film used in theconventional polarizing film may be used. A material of such a PVA-basedfilm may include PVA or a derivative thereof. The derivative of PVA mayinclude polyvinylformal or polyvinyl acetal, and the like, and may alsoinclude those modified by olefins such as ethylene or propylene,unsaturated carboxylic acids such as acrylic acid, methacrylic acid orcrotonic acid and alkyl esters thereof or acrylamide, and the like. ThePVA has a polymerization degree of about 100 to 10000 or so or about1000 to 10000 or so, and a saponification degree of about 80 mol % to100 mol % or so, but is not limited thereto.

The PVA-based film can also be exemplified by a hydrophilic polymer filmsuch as a partially saponified film of ethylene-vinyl acetate copolymerseries, a polyene-based oriented film such as a dehydrated product ofPVA or a dehydrochlorinated product of polyvinyl chloride, and the like.

The PVA-based film may contain an additive such as a plasticizer or asurfactant. The plasticizer may be exemplified by polyol and acondensate thereof, and for example, may be exemplified by glycerin,diglycerin, triglycerin, ethylene glycol, propylene glycol orpolyethylene glycol, and the like. When such a plasticizer is used, theratio thereof is not particularly limited and may be generallyapproximately 20 wt % or less in the PVA-based film.

The kind of the anisotropic absorbent material that can be included inthe polarizing film is also not particularly limited. In the presentapplication, among the known anisotropic absorbent materials, thosecapable of satisfying the above-described optical characteristics can beappropriately selected. An example of the anisotropic absorbent materialcan be exemplified by iodine. The ratio of the anisotropic absorbentmaterial in the polarizing film is also not particularly limited as longas it can satisfy the desired physical properties.

The polarizing film can be produced, for example, by performing at leastdyeing, cross-linking and stretching processes on the PVA-based film.

In the dyeing process, an anisotropic absorbent material such as iodinecan be adsorbed and/or oriented on the PVA-based film. Such a dyeingprocess can be performed together with the stretching process. Thedyeing can generally be carried out by immersing the film in a solutioncontaining an anisotropic absorbent material, for example, an iodinesolution. As the iodine solution, for example, an aqueous solution inwhich iodine ions are contained by iodine and an iodinated compound as asolubilizing agent may be used. Here, as the iodinated compound, forexample, potassium iodide, lithium iodide, sodium iodide, zinc iodide,aluminum iodide, lead iodide, copper iodide, barium iodide, calciumiodide, tin iodide or titanium iodide, and the like can be used. Theconcentrations of iodine and/or iodide ions in the iodine solution canbe controlled within a conventional range according to the purpose. Inthe dyeing process, the temperature of the iodine solution is usually20° C. to 50° C. or 25° C. to 40° C. or so, and the immersion time isusually 10 seconds to 300 seconds or 20 seconds to 240 seconds or so,without being limited thereto.

The cross-linking process carried out in the production procedure of thepolarizing film can be carried out, for example, using a cross-linkingagent such as a boron compound. The order of the cross-linking processis not particularly limited, and the process can be performed, forexample, with the dyeing and/or stretching processes, or can proceedseparately. The cross-linking process may also be carried out severaltimes. As the boron compound, boric acid or borax may be used. The boroncompound can be generally used in the form of an aqueous solution or amixed solution of water and an organic solvent, and usually an aqueoussolution of boric acid is used. The boric acid concentration in theboric acid aqueous solution can be selected in an appropriate range inconsideration of the cross-linking degree and the heat resistancethereof. An iodinated compound such as potassium iodide can be containedin an aqueous solution of boric acid or the like.

The treatment temperature of the cross-linking process is usually in arange of 25° C. or higher, 30° C. to 85° C. or 30° C. to 60° C. or so,and the treatment time is usually 5 seconds to 800 seconds or 8 secondsto 500 seconds or so, without being limited thereto.

The stretching process is generally performed by uniaxial stretching.Such stretching may also be performed together with the dyeing and/orcross-linking processes. The stretching method is not particularlylimited, and for example, a wet stretching method can be applied. Insuch a wet stretching method, for example, stretching after dyeing isgenerally carried out, but stretching may be carried out together withcross-linking, and may be carried out several times or in multiplestages.

The iodinated compound such as potassium iodide can be contained in thetreatment liquid applied to the wet stretching method. In thestretching, the treatment temperature is usually in the range of 25° C.or higher, 30° C. to 85° C., or 50° C. to 70° C. or so, and thetreatment time is usually 10 seconds to 800 seconds or 30 seconds to 500seconds, without being limited thereto.

The total draw ratio in the stretching processes can be controlled inconsideration of the orientation characteristics and the like, and thetotal draw ratio may be about 3 to 10 times, 4 to 8 times, or 5 to 7times or so based on the original length of the PVA-based film, but isnot limited thereto. Here, in the case of involving the stretching evenin the swelling process or the like other than the stretching process,the total draw ratio may mean the cumulative draw ratio including thestretching in each process. Such a total draw ratio can be adjusted toan appropriate range in consideration of orientation, workability orstretching cut possibility of the polarizing film, and the like. Theshrinkage force can be controlled by controlling the draw ratio, asdescribed above.

In the production process of the polarizing film, in addition to thedyeing, cross-linking and stretching, the swelling process may also beperformed before the processes are performed. It is possible to cleancontamination of the PVA-based film surface, or an antiblocking agent byswelling, and there is also an effect capable of reducing unevennesssuch as dyeing deviation by the swelling.

In the swelling process, water, distilled water or pure water, and thelike can be usually used. The main component of the relevant treatmentliquid is water, and if necessary, a small amount of an iodinatedcompound such as potassium iodide or an additive such as a surfactant,or alcohol, and the like can be included therein.

The treatment temperature in the swelling process is usually 20° C. to45° C. or so, or 20° C. to 40° C. or so, but is not limited thereto.Since the swelling deviations can cause dyeing deviations, the processvariables can be adjusted so that the occurrence of such swellingdeviations is suppressed as much as possible. If necessary, the properstretching may also be performed in the swelling process. The draw ratiomay be 6.5 times or less, 1.2 to 6.5 times, 2 times to 4 times, or 2times to 3 times, based on the original length of the PVA-based film.The stretching in the swelling process can control the stretching in thestretching process performed after the swelling process to be small andcan control so that the stretching failure of the film does not occur.

In the production process of the polarizing film, a metal ion treatmentcan be performed. Such a treatment is carried out, for example, byimmersing the PVA-based film in an aqueous solution containing a metalsalt. This allows metal ions to be contained in the polarizer, and inthis process, the color tone of the PVA-based polarizing film can alsobe adjusted by controlling the kind or ratio of the metal ions. As themetal ion that can be applied, metal ions of transition metals such ascobalt, nickel, zinc, chromium, aluminum, copper, manganese or iron canbe exemplified, and the color tone can also be adjusted by selecting aproper kind among them.

In the production procedure of the polarizing film, the cleaning processmay proceed after dyeing, cross-linking and stretching. Such a cleaningprocess may be performed by a solution of iodine compound such aspotassium iodide, and may also be performed by using water.

This cleaning with water may also be combined with cleaning with thesolution of an iodinated compound, where a solution in which liquidalcohols such as methanol, ethanol, isopropyl alcohol, butanol orpropanol are blended may also be used.

After passing through such a process, the polarizing film can beproduced by performing a drying process. In the drying process, forexample, it may be performed at an appropriate temperature for asuitable time in consideration of the moisture content and the likerequired for the polarizing film, and such conditions are notparticularly limited.

The thickness of the polarizing film applied in the present applicationmay usually be within a range of about 5 μm to 25 μm. In anotherexample, the thickness may be about 24 μm or less, 23 μm or less, 22 μmor less, 21 μm or less, 20 μm or less, 19 μm or less, 18 μm or less, or17 μm or less, or may be about 6 μm or more, 7 μm or more, 8 μm or more,9 μm or more, 10 μm or more, 11 μm or more, 12 μm or more, 13 μm ormore, 14 μm or more, 15 μm or more, or 16 μm or more or so.

The polarizing film may have shrinkage force in one in-plane directionwithin a range of about 0.1N to 15N. The one in-plane direction may be,for example, a direction in which the above-described light absorptionaxis is formed. The shrinkage force may be 14.5 N or less, 14 N or less,13.5 N or less, 13 N or less, 12.5 N or less, 12 N or less, 11.5 N orless, 11 N or less, 10.5 N or less, 10 N or less, 10 N or less, 9.5 N orless, or 9 N or less, or may be 0.5 N or more, 1 N or more, 2 N or more,3 N or more, 4 N or more, 5 N or more, 6 N or more, 7 N or more, or 8Nor more.

The polarizing film having the shrinkage force as above can be appliedby selecting the polarizing film having the shrinkage force among theavailable polarizing films or by controlling the process conditions suchas the stretching conditions in the production procedure as describedabove. Usually, the polarizing film produced using the PVA-based filmexhibits the shrinkage force in the above-mentioned range in the lightabsorption axis direction, and thus the polarizing film produced fromthe PVA-based film in the present application, that is, the PVA-basedpolarizing film can generally be used.

In the production method of the present application, the step ofattaching the polarizing film as above and the optical film isperformed.

In the production method of the present application, the attachment ofthe polarizing film and the optical film may be performed such that theratio (S_(P)/S_(V)) of the shrinkage force (S_(P)) of the entirepolarizing plate in the light absorption axis direction of thepolarizing film to the shrinkage force (S_(V)) of the entire polarizingplate in the direction perpendicular to the light absorption axisdirection is in the range of 0.7 to 1.5. In another example, the ratio(S_(P)/S_(V)) may be about 0.71 or more, about 0.72 or more, about 0.73or more, about 0.74 or more, about 0.75 or more, about 0.76 or more,about 0.77 or more, about 0.78 or more, about 0.79 or more, about 0.8 ormore, about 0.81 or more, about 0.82 or more, about 0.83 or more, about0.84 or more, about 0.85 or more, about 0.86 or more, about 0.87 ormore, about 0.88 or more, about 0.89 or more, about 0.9 or more, about0.91 or more, about 0.92 or more, about 0.93 or more, about 0.94 ormore, about 0.95 or more, about 0.96 or more, or about 0.97 or more, ormay be about 1.49 or less, about 1.48 or less, about 1.47 or less, about1.46 or less, about 1.45 or less, about 1.44 or less, about 1.43 orless, about 1.42 or less, about 1.41 or less, about 1.4 or less, about1.39 or less, about 1.38 or less, about 1.37 or less, about 1.36 orless, about 1.35 or less, about 1.34 or less, about 1.33 or less, about1.32 or less, about 1.31 or less, about 1.30 or less, about 1.29 orless, about 1.28 or less, about 1.27 or less, about 1.26 or less, about1.25 or less, about 1.24 or less, about 1.23 or less, about 1.22 orless, about 1.21 about 1.2 or less, about 1.19 or less, about 1.18 orless, about 1.17 or less, about 1.16 or less, about 1.15 or less, about1.14 or less, about 1.13 or less, about 1.12 or less, about 1.11 orless, about 1.1 or less, about 1.09 or less, about 1.08 or less, about1.07 or less, or about 1.06 or less. By adjusting the ratio, apolarizing plate capable of preventing bending or twisting can be formedregardless of the desired polarizing plate, that is, the thickness andthe light absorption axis direction and the size of the polarizingplate, and the like.

In the production method of the present application, the attachment ofthe polarizing film and the optical film may also be performed such thatthe shrinkage force of the entire polarizing plate in the directionparallel to the light absorption axis of the polarizing film is in therange of 6.5N to 15N. In another example, the shrinkage force may beabout 6.6N or more, 6.7N or more, 6.8N or more, 6.9N or more, 7N ormore, 7.1N or more, 7.2N or more, 7.3N or more, 7.4N or more, 7.5N ormore, 7.6N or more, or 7.7N or more, or may be 14.9N or less, 14.8N orless, 14.7N or less, 14.6N or less, 14.5N or less, 14.4N or less, 14.3Nor less, 14.2N or less, 14.1N or less, 14N or less, 13.9N or less, 13.8Nor less, 13.7N or less, 13.6N or less, 13.5N or less, 13.4N or less,13.3N or less, 13.2N or less, 13.1N or less, 13N or less, 12.9N or less,12.8N or less, 12.7N or less, 12.6N or less, 12.5N or less, 12.4N orless, 12.3N or less, 12.2N or less, 12.1N or less, 12N or less, 11.9N orless, 11.8N or less, 11.7N or less, 11.6N or less, 11.5N or less, 11.4Nor less, 11.3N or less, 11.2N or less, 11.1N or less, 11N or less, 10.9Nor less, 10.8N or less, 10.7N or less, 10.6N or less, 10.5N or less,10.4N or less, 10.3N or less, 10.2N or less, 10.1N or less, 10N or less,9.9N or less, 9.8N or less, 9.7N or less, 9.6N or less, 9.5N or less,9.4N or less, 9.3N or less, 9.2 N or less, 9.1N or less, 9N or less,8.9N or less, 8.8N or less, 8.7N or less, 8.6N or less, 8.5N or less,8.4N or less, 8.3N or less, 8.2N or less, or 8.1N or less. By adjustingthe ratio, a polarizing plate capable of preventing bending or twistingcan be formed regardless of the desired polarizing plate, that is, thethickness and the light absorption axis direction and the size of thepolarizing plate, and the like.

The production method of the present application may also be performedsuch that the shrinkage force of the entire polarizing plate in thedirection perpendicular to the light absorption axis of the polarizingfilm is in the range of 6N to 15N. In another example, the shrinkageforce may be about 6.1N or more, about 6.2N or more, about 6.3N or more,about 6.4N or more, about 6.5N or more, 6.6N or more, 6.7N or more, 6.8Nor more, 6.9N or more, 7N or more, 7.1N or more, or 7.2N or more, or maybe 14.9N or less, 14.8N or less, 14.7N or less, 14.6N or less, 14.5N orless, 14.4N or less, 14.3N or less, 14.2N or less, 14.1N or less, 14N orless, 13.9N or less, 13.8N or less, 13.7N or less, 13.6N or less, 13.5Nor less, 13.4N or less, 13.3N or less, 13.2N or less, 13.1N or less, 13Nor less, 12.9N or less, 12.8N or less, 12.7N or less, 12.6N or less,12.5N or less, 12.4N or less, 12.3N or less, 12.2N or less, 12.1N orless, 12N or less, 11.9N or less, 11.8N or less, 11.7N or less, 11.6N orless, 11.5N or less, 11.4N or less, 11.3N or less, 11.2N or less, 11.1Nor less, 11N or less, 10.9N or less, 10.8N or less, 10.7N or less, 10.6Nor less, 10.5N or less, 10.4N or less, 10.3N or less, 10.2N or less,10.1N or less, 10N or less, 9.9N or less, 9.8N or less, 9.7N or less,9.6N or less, 9.5N or less, 9.4N or less, 9.3N or less, 9.2N or less,9.1N or less, 9N or less, 8.9N or less, 8.8N or less, 8.7N or less, 8.6Nor less, 8.5N or less, 8.4N or less, 8.3N or less, 8.2N or less, or 8.1Nor less. By adjusting the ratio, a polarizing plate capable ofpreventing bending or twisting can be formed regardless of the desiredpolarizing plate, that is, the thickness and the light absorption axisdirection and the size of the polarizing plate, and the like.

In order to form such a polarizing plate, the attachment position may becontrolled when the optical film and the polarizing film are attached.For example, the attachment may be performed such that the firstdirection of the polymer film, that is, the direction (for example, theTD direction of the polymer film) in which the shrinkage force after theheat-treatment is in the range of 5N to 10N and the light absorptionaxis of the polarizing film are perpendicular to each other.

Therefore, the ratio (S1/S2) of the shrinkage force (S1) of the polymerfilm, which is applied in the attachment process, in the first directionand the shrinkage force (S2) in the second direction perpendicular tothe first direction (the ratio after the heat-treatment) may be 13 ormore.

Specific details of the shrinkage force of the polymer film or theoptical film in the first direction after the heat-treatment, the ratio(S1/S2) of shrinkage force, and other properties are as described above.

In view of the above-mentioned shrinkage force of the polarizing film inthe light absorption axis direction, the ratio (S_(Pro)/S_(PVA)) of theshrinkage force (S_(PVA)) of the polarizing film in the in-planedirection parallel to the light absorption axis direction and theshrinkage force (S_(Pro)) of the optical film (polymer film) in thefirst direction by such an attachment process may be in the range of 0.1to 5. In another example, the ratio may be about 0.15 or more, about 0.2or more, about 0.25 or more, about 0.3 or more, about 0.35 or more,about 0.4 or more, about 0.45 or more, about 0.5 or more, about 0.55 ormore, about 0.6 or more, or about 0.65 or more, or may be about 4.5 orless, about 4 or less, about 3.5 or less, about 3 or less, about 2.5 orless, about 2 or less, about 1.5 or less, about 1 or less, about 0.95 orless, about 0.9 or less, about 0.85 or less, about 0.8 or less, or about0.75 or less or so.

Through the arrangement as above, the present application can provide apolarizing plate without any problem of durability, warpage or twisting,regardless of the thickness, the formation direction of the lightabsorption axis and the size of the polarizing plate.

For example, the production process of the polarizing plate may beperformed such that the range of the A value according to Equation 1below is in a range of 0.01 to 26 N·mm. That is, by adjusting thethicknesses of the optical film, the pressure-sensitive adhesive layerand/or the polarizing film or the thickness of each element included inthe polarizing plate in addition to the above in consideration of theshrinkage force of the optical film and the polarizing film applied atthe time of producing the polarizing plate, it is possible to satisfyEquation 1 below. The production process of the polarizing plate thatsatisfies Equation 1 may further comprising a process of forming apressure-sensitive adhesive layer on the surface of the polarizing filmon which the optical film is not attached.

A=a X(S _(PVA) X(T ₁ +b)+S _(Pro) X(T ₂ +b))  [Equation 1]

In Equation 1, S_(PVA) is the shrinkage force of the polarizing film inthe light absorption axis direction, S_(Pro) is the large shrinkageforce among the shrinkage force of the optical film in the directionparallel to the light absorption axis direction of the polarizing filmand the shrinkage force of the optical film in the directionperpendicular to the light absorption direction, T₁ is the distance(unit: mm) from the lowermost portion of the pressure-sensitive adhesivelayer to the center of the polarizing film, T₂ is the distance (unit:mm) from the lowermost portion of the pressure-sensitive adhesive layerto the center of the optical film, a is a number within a range of 0.5to 2, and b is a number within a range of 0.14 to 0.6.

The A value in Equation 1 above reflects a bending property of thepolarizing plate. If the polarizing plate has the A value, even when thepolarizing plate is formed thin, it is possible to provide a displaydevice having excellent durability and optical characteristics withoutcausing warping or twisting upon having been applied to a display devicesuch as an LCD or an OLED.

In another example, the A value in Equation 1 above may be 0.05 N·mm ormore, 0.1 N·mm or more, 0.15 N·mm or more, 0.2 N·mm or more, 0.25 N·mmor more, 0.3 N·mm or more, 0.4 N·mm or more, 0.45 N·mm or more, 0.5 N·mmor more, 0.55 N·mm or more, 0.6 N·mm or more, 0.65 N·mm or more, 0.7N·mm or more, 0.75 N·mm or more, 0.8 N·mm or more, 0.85 N·mm or more,0.9 N·mm or more, 0.95 N·mm or more, 0.1 N·mm or more, 0.5 N·mm or more,1 N·mm or more, 1.5 N·mm or more, 2 N·mm or more, 2.5 N·mm or more, 3N·mm or more, 3.5 N·mm or more, 4 N·mm or more, 4.5 N·mm or more, 5 N·mmor more, 5.5 N·mm or more, 6 N·mm or more, 6.5 N·mm or more, 7 N·mm ormore, 7.5 N·mm or more, 8 N·mm or more, 8.5 N·mm or more, 9 N·mm ormore, 9.5 N·mm or more, 10 N·mm or more, 11 N·mm or more, 12 N·mm ormore, 13 N·mm or more, 14 N·mm or more, 15 N·mm or more, 16 N·mm ormore, 17 N·mm or more, 18 N·mm or more, 19 N·mm or more, or 20 N·mm ormore or so, or may be 25 N·mm or less, 24 N·mm or less, 23 N·mm or less,22 N·mm or less, 21 N·mm or less, 20 N·mm or less, 19 N·mm or less, 18N·mm or less, 17 N·mm or less, 16 N·mm or less, 15 N·mm or less, 14 N·mmor less, 13 N·mm or less, 12 N·mm or less, 11 N·mm or less, 10 N·mm orless, 9 N·mm or less, 8 N·mm or less, 7 N·mm or less, 6 N·mm or less, or5 N·mm or less.

The A value may fall within the above-described numerical range in theentire range of a and/or b, as defined above, or may also fall withinthe above-described numerical range when any one value within the rangeof a and any one value within the range of b have been substituted.

In Equation 1 above, the a value may be a number in a range of 0.5 to 2.In another example, the a value may be about 0.55 or more, about 0.6 ormore, about 0.65 or more, about 0.7 or more, about 0.75 or more, about0.8 or more, about 0.85 or more, about 0.9 or more, about 1 or more, orabout 1.5 or more, or may also be 1.9 or less, about 1.8 or less, about1.7 or less, about 1.6 or less, about 1.5 or less, about 1.4 or less,about 1.3 or less, about 1.2 or less, about 1.1 or less, about 1.0 orless, about 0.95 or less, about 0.9 or less, about 0.85 or less, about0.8 or less, about 0.75 or less, about 0.7 or less, or about 0.65 orless.

In Equation 1 above, the b value may be a number in a range of 0.14 to0.6. In another example, the b value to be substituted in Equation 1above may be 0.15 or more, or 0.2 or more, or may be 0.55 or less, 0.5or less, 0.45 or less, 0.4 or less, 0.35 or less, or 0.3 or less. In oneexample, when the polarizing plate is applied to an LCD, the b value maybe determined according to the thickness of the LCD panel, and forexample, a half of the thickness (unit: mm) of the LCD panel may be theb value.

For example, in the method for producing the polarizing plate, theattachment of the optical film and the polarizing film may be performedusing a known adhesive. Therefore, in the polarizing plate, an adhesivelayer may be further included between the optical film and thepolarizing film.

As the adhesive, for example, an adhesive layer used for attaching apolarizing film and an optical film in a conventional polarizing platecan be used.

The adhesive layer may comprise one or two or more of, for example, apolyvinyl alcohol-based adhesive; an acrylic adhesive; a vinylacetate-based adhesive; a urethane-based adhesive; a polyester-basedadhesive; a polyolefin-based adhesive; a polyvinyl alkyl ether-basedadhesive; a rubber-based adhesive; a vinyl chloride-vinyl acetate-basedadhesive; a styrene-butadiene-styrene (SBS) adhesive; astyrene-butadiene-styrene hydrogen adduct (SEBS)-based adhesive; anethylenic adhesive; and an acrylic ester-based adhesive, and the like.Such an adhesive may be formed using, for example, an aqueous,solvent-based or solventless adhesive composition. In addition, theadhesive composition may be a thermosetting type, room temperaturecuring type, moisture curing type, active energy ray curing type orhybrid curing type adhesive composition.

The manner of attaching a polarizing film and an optical film using suchan adhesive is not particularly limited, and a manner of applying theadhesive composition to the polarizing film or the optical film,laminating the polarizing film and the optical film, and curing thesame, or a droplet manner can be used.

The thickness of such an adhesive layer can be, for example, in a rangeof about 1 μm to 5 μm or about 2 μm to 4 μm.

The polarizing plate of the present application as above may compriseother necessary constitutions in addition to the above-describedelements.

As a further constitution, the polarizing plate may further comprise acured resin layer or other types of protective films of the polarizingfilm between the polarizing film and the pressure-sensitive adhesivelayer. Although the cured resin layer is more advantageous than theprotective film for forming a thinner polarizing plate, the protectivefilm may also be applied. Such a cured resin layer is also generallycalled a hard coating layer, and is generally applied instead ofomitting any one of optical films in a polarizing plate. The kind of thecured resin layer that can be applied in the present application is notparticularly limited, and various types of cured resin layers used forproviding the thin polarizing plate can be applied. Usually, such acured resin layer may comprise an epoxy resin, an oxetane resin, aurethane resin and/or an acrylic resin, and the like, and such a resinlayer is variously known.

The thickness of this cured resin layer can be, for example, in a rangeof about 4 μm to 10 μm or about 4.5 μm to 10 μm.

The kind of protective film is also not particularly limited, which maybe appropriately selected from known materials.

As described above, the polarizing plate of the present application mayalso further comprise one or more functional layers selected from thegroup consisting of other known constitutions, for example, aretardation plate, a wide viewing angle compensation film, and/or abrightness enhancing film, and thus, the production method may alsocomprise a step of forming such functional layers in the requiredpositions.

The polarizing plate may be configured in various forms according to theapplication to be applied, for example, the type of the applied displaydevice or the mode of the relevant device.

For example, the small angle of the angles formed by one side of thepolarizing film in the polarizing plate and the light absorption axis ofthe polarizing film may be in a range of 0 degrees to 10 degrees or in arange of 80 degrees to 100 degrees. In another example, the angle may be9 degrees or less, 8 degrees or less, 7 degrees or less, 6 degrees orless, 5 degrees or less, 4 degrees or less, 3 degrees or less, 2 degreesor less, or 1 degree or less. Furthermore, in another example, the anglemay be about 81 degrees or more, 82 degrees or more, 83 degrees or more,84 degrees or more, 85 degrees or more, 86 degrees or more, 87 degreesor more, 88 degrees or more, 89 degrees or more, or 90 degrees or more,or may also be 99 degrees or less, 98 degrees or less, 97 degrees orless, 96 degrees or less, 95 degrees or less, 94 degrees or less, 93degrees or less, 92 degrees or less, 91 degrees or less, or about 90degrees or less or so.

In another example, the small angle of the angles formed by one side ofthe polarizing film in the polarizing plate and the light absorptionaxis of the polarizing film may be in the range of 35 degrees to 55degrees or in the range of 125 degrees to 145 degrees.

In another example, the angle may be about 36 degrees or more or so, 37degrees or more or so, 38 degrees or more or so, 39 degrees or more orso, 40 degrees or more or so, 41 degrees or more or so, 42 degrees ormore or so, 43 degrees or more or so, 44 degrees or more or so, or 45degrees or more or so, or may be 54 degrees or less or so, 53 degrees orless or so, 52 degrees or less or so, 51 degrees or less or so, 50degrees or less or so, 49 degrees or less or so, 48 degrees or less orso, 47 degrees or less or so, 46 degrees or less or so, or 45 degrees orless or so, and furthermore, may be about 126 degrees or more or so, 127degrees or more or so, 128 degrees or more or so, 129 degrees or more orso, 130 degrees or more or so, 131 degrees or more or so, 132 degrees ormore or so, 133 degrees or more or so, 134 degrees or more or so, or 135degrees or more or so, or may be 144 degrees or less or so, 143 degreesor less, 142 degrees or less or so, 141 degrees or less or so, 140degrees or less or so, 139 degrees or less or so, 138 degrees or less orso, 137 degrees or less or so, 136 degrees or less or so, or 135 degreesor less or so.

Usually, the polarizing film and the polarizing plate may have aquadrangle, and one side of the polarizing film or the polarizing plateforming the angle with the light absorption axis may be any one side ofthe quadrangle. For example, if the quadrangle is a rectangle, the oneside may be a long side or a short side of the rectangle.

In the case of the present application, a polarizing plate having properperformance may be provided regardless of how the light absorption axisis formed depending on the application of the polarizing plate.

The present application also relates to a display device, and forexample, relates to an LCD or OLED. The display device such as the LCDor the OLED may comprise the polarizing plate of the presentapplication. The display device may comprise, for example, a displaypanel such as an LCD panel or an OLED panel and the polarizing plate ofthe present application attached to the display panel.

The type of the display panel applicable to the display device of thepresent application or the position of the polarizing plate attached tothe panel, and the like is not particularly limited. That is, thedisplay panel can be realized in various known manners as long as thepolarizing plate of the present application is applied.

Advantageous Effects

The present application can provide an optical film satisfying opticaland mechanical durability required in a polarizing plate effectively andcapable of forming a polarizing plate without causing bending whenapplied to a display device, and a method for producing a polarizingplate to which the optical film is applied. The present application canprovide an optical film capable of realizing the required optical andmechanical durability without causing bending even in a polarizing plateapplied to a thin display device and/or a thin polarizing plate, and amethod for producing a polarizing plate to which the optical film isapplied.

MODE FOR INVENTION

Hereinafter, the present application will be described in detail throughExamples, but the scope of the present application is not limited by thefollowing Examples.

The term MD referred to herein means the machine direction of thestretched film unless otherwise specified, and the TD means thetransverse direction of the stretched film unless otherwise specified.

1. Measurement of Shrinkage Force

The shrinkage force of the polarizing film, the optical film, thepolymer film or the polarizing plate mentioned herein was measured bythe following method using a DMA instrument from TA. A specimen wasproduced to have a width of about 5.3 mm and a length of about 15 mm,and both ends of the specimen in the longitudinal direction were fixedto the clamp of the measuring instrument and then the contractile forcewas measured. Here, the length 15 mm of the specimen is the lengthexcluding the portion to be fixed to the clamp. After fixing thespecimen to the clamp as above, the specimen was pulled and fixed tomaintain strain 0.1% in the state of preload 0N, and then the shrinkageforce applied when the strain 0.1% was kept at the elevated temperatureof the following temperature condition was measured. As the results ofthe shrinkage force, values were measured 120 minutes after 80° C.stabilization of the following temperature condition. The shrinkageforce was measured at relative humidity maintained at approximately 48%or so.

<Measurement Temperature Condition and Time>

Temperature: 25° C. start→75° C. after 3 minutes→80° C. stabilization(no acceleration condition) after 7 minutes

Measurement time: 120 minutes

Production Example 1. Production of PVA-Based Polarizing Film (A)

After a PVA (poly(vinyl alcohol)) film (Nippon Synthetic Chemical Co.,Ltd., polymerization degree of about 3,000 or so) with a thickness ofabout 45 μm or so used in manufacturing a polarizing film was swelled ina pure solution at a temperature ranging from about 20° C. to 30° C., adyeing process was performed for about 10 seconds to 30 seconds or so inan iodine solution at a temperature of 30° C. to 40° C. or so.Thereafter, a cleaning process was performed for about 20 seconds with aboric acid solution (concentration: about 2 wt %) at a temperature ofabout 40° C. or so, and then the film was stretched about 6 times in aboric acid solution at a temperature of 50° C. to 60° C. and aconcentration of about 4.0 wt %, and after stretching, a complementarycolor process was performed in a KI solution at a concentration of about2 to 4 wt % and dried to produce a polarizing film having a thickness ofabout 17 μm. As a result of measuring the shrinkage force (hereinafter,MD shrinkage force) of the manufactured PVA-based polarizing film in thelight absorption axis direction, it was approximately 8 to 10 N or so.

Example 1

Heat Treatment of Polymer Film

For a PET (polyethylene terephthalate) polymer film (SRF film,thickness: 80 μm, manufacturer: Toyobo, product name: TA055, glasstransition temperature: 80° C., shrinkage force in TD direction beforeheat-treatment: about 7.53 N, shrinkage direction in MD direction: in arange of about 0.1 to 0.5N), heat-treatment was performed in thefollowing manner. First, a flattening process was performed by exposingthe SRF film to steam having a temperature of approximately 80° C. to100° C. or so for a time (about 20 seconds to 60 seconds) to improveflatness. Subsequently, an antiglare layer (AG layer) as an opticallayer was formed on one side of the SRF film. The antiglare layer wasformed by using a curable composition, in which organic particles(manufacturer: Sekisui, average diameter: 2 μm) having a refractiveindex in a level of about 1.555 (reference wavelength: 550 nm) and ahydroxyl group on the surface were mixed to a urethane acrylate binder(Kyoeisha, PE3A) in a weight ratio of 20:1 (urethane acrylate binder:organic particles). The binder was crosslinked and polymerized bycoating the curable composition on one side of the SRF film andirradiating it with ultraviolet rays in a light quantity of 150 mJ/cm²,thereby forming an optical layer, where the antiglare layer thus formedhad a thickness of approximately 4 μm or so.

Subsequently, the SRF film on which the optical layer was formed wasmaintained at a temperature of approximately 40° C. or so for 30 secondsto 90 seconds to perform heat-treatment. After the heat-treatmentprocess, the shrinkage force of the SRF film in the TD (transversedirection) direction was about 7.18N or so, and the shrinkage force inthe MD direction was in a level of about 0.2 to 0.35N or so.

Manufacture of Polarizing Plate

The heat-treated SRF film was applied as a protective film to produce apolarizing plate in the following manner. First, the SRF film wasattached to one side of the PVA polarizing film (MD shrinkage: 8 to 10N, thickness: 17 μm) produced in Production Example 1 using anepoxy-based ultraviolet curable adhesive (thickness: 2 μm to 3 μm). Uponthe attachment, they were attached such that the TD (transversedirection) direction of the SRF film and the MD direction (absorptionaxis direction) of the PVA polarizing film were approximatelyperpendicular to each other, where the surface on which the opticallayer was not formed was attached to the PVA polarizing film.Subsequently, an epoxy-based hard coating layer was formed to athickness of about 5 to 7 μm or so on the surface of the PVA polarizingfilm to which the SRF film was not attached. Thereafter, an acrylicpressure-sensitive adhesive layer having a thickness of about 25 μm wasformed on the lower part of the hard coating layer to produce apolarizing plate. The shrinkage force of the entire polarizing plate asmanufactured above along the MD direction of the polarizing film wasapproximately 8N, and the shrinkage force along the TD direction of thepolarizing film was approximately 9.5N or so. As a result of obtainingthe A value of Equation 1 above on the manufactured polarizing plate, itwas approximately 3.94 Nmm to 6.41 Nmm or so. The lower limit of the Avalue range was obtained by applying 0.78 as a, applying 0.25 mm(=applied LCD panel thickness (mm)/2) as b, applying about 9 N asS_(PVA), applying 7.18N as S_(Pro), applying 0.0395 mm(=pressure-sensitive adhesive thickness (25 μm)+hard coating layerthickness (6 μm)+polarizing film thickness (17 μm)/2) as T1, andapplying 0.0905 mm (=pressure-sensitive adhesive thickness (25 μm)+hardcoating layer thickness (6 μm)+polarizing film thickness (17μm)+adhesive layer thickness (2.5 μm)+protective film thickness (80μm)/2) as T2, in Equation 1. In addition, the upper limit of the A valuerange was obtained by applying 1.27 as a, applying 0.25 mm (=applied LCDpanel thickness (mm)/2) as b, applying about 9 N as S_(PVA), applying7.18N as S_(Pro), applying 0.0395 mm (=pressure-sensitive adhesivethickness (25 μm)+hard coating layer thickness (6 μm)+polarizing filmthickness (17 μm)/2) as T1, and applying 0.0905 mm (=pressure-sensitiveadhesive thickness (25 μm)+hard coating layer thickness (6μm)+polarizing film thickness (17 μm)+adhesive layer thickness (2.5μm)+protective film thickness (80 μm)/2) as T2, in Equation 1.

Example 2

Heat treatment was performed by maintaining the SRF film subjected tothe steam treatment and the optical layer formation treatment in thesame manner as in Example 1 at a temperature of approximately 60° C. orso for 30 seconds to 90 seconds. After the heat-treatment process, theshrinkage force of the SRF film in the TD (transverse direction)direction was about 6.86N or so, and the shrinkage force in the MDdirection was in a level of about 0.2 to 0.35N or so. The polarizingplate was produced in the same manner as in Example 1 using the SRFfilm. The shrinkage force of the produced polarizing plate along the MDdirection of the polarizing film was approximately 8N, and the shrinkageforce along the TD direction of the polarizing film was approximately8.18N or so. As a result of obtaining the A value of Equation 1 above onthe manufactured polarizing plate, it was approximately 4.25 Nmm to 5.78Nmm or so. The lower limit of the A value range was obtained by applying0.86 as a, applying 0.25 mm (=applied LCD panel thickness (mm)/2) as b,applying about 9 N as S_(PVA), applying 6.86N as S_(Pro), applying0.0395 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coatinglayer thickness (6 μm)+polarizing film thickness (17 μm)/2) as T1, andapplying 0.0905 mm (=pressure-sensitive adhesive thickness (25 μm)+hardcoating layer thickness (6 μm)+polarizing film thickness (17μm)+adhesive layer thickness (2.5 μm)+protective film thickness (80μm)/2) as T2, in Equation 1. In addition, the upper limit of the A valuerange was obtained by applying 1.17 as a, applying 0.25 mm (=applied LCDpanel thickness (mm)/2) as b, applying about 9 N as S_(PVA), applying6.86N as S_(Pro), applying 0.0395 mm (=pressure-sensitive adhesivethickness (25 μm)+hard coating layer thickness (6 μm)+polarizing filmthickness (17 μm)/2) as T1, and applying 0.0905 mm (=pressure-sensitiveadhesive thickness (25 μm)+hard coating layer thickness (6μm)+polarizing film thickness (17 μm)+adhesive layer thickness (2.5μm)+protective film thickness (80 μm)/2) as T2, in Equation 1.

Example 3

Heat treatment was performed by maintaining the SRF film subjected tothe steam treatment and the optical layer formation treatment in thesame manner as in Example 1 at a temperature of approximately 80° C. forabout 30 seconds to 90 seconds. After the heat-treatment process, theshrinkage force of the SRF film in the TD (transverse direction)direction was about 6.08N or so, and the shrinkage force in the MDdirection was in a level of about 0.2 to 0.35N or so. The polarizingplate was produced in the same manner as in Example 1 using the SRFfilm. The shrinkage force of the produced polarizing plate along the MDdirection of the polarizing film was approximately 8N, and the shrinkageforce along the TD direction of the polarizing film was approximately7.28N or so.

As a result of obtaining the A value of Equation 1 above on themanufactured polarizing plate, it was approximately 3 Nmm to 7.25 Nmm orso. The lower limit of the A value range was obtained by applying 0.64as a, applying 0.25 mm (=applied LCD panel thickness (mm)/2) as b,applying about 9 N as S_(PVA), applying 6.08N as S_(Pro), applying0.0395 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coatinglayer thickness (6 μm)+polarizing film thickness (17 μm)/2) as T1, andapplying 0.0905 mm (=pressure-sensitive adhesive thickness (25 μm)+hardcoating layer thickness (6 μm)+polarizing film thickness (17μm)+adhesive layer thickness (2.5 μm)+protective film thickness (80μm)/2) as T2, in Equation 1. In addition, the upper limit of the A valuerange was obtained by applying 1.55 as a, applying 0.25 mm (=applied LCDpanel thickness (mm)/2) as b, applying about 9 N as S_(PVA), applying6.08N as S_(Pro), applying 0.0395 mm (=pressure-sensitive adhesivethickness (25 μm)+hard coating layer thickness (6 μm)+polarizing filmthickness (17 μm)/2) as T1, and applying 0.0905 mm (=pressure-sensitiveadhesive thickness (25 μm)+hard coating layer thickness (6μm)+polarizing film thickness (17 μm)+adhesive layer thickness (2.5μm)+protective film thickness (80 μm)/2) as T2, in Equation 1.

Bending Characteristic Evaluation

The polarizing plates manufactured in Examples were each attached to theupper and lower surfaces of a general 32-inch LCD (liquid crystaldisplay) panel (thickness: about 500 μm) through the pressure-sensitiveadhesive layers of the polarizing plates, respectively. Subsequently,the flatness (initial flatness) of the LCD panel was measured.Thereafter, the panel was put into a chamber at a temperature of 60° C.for 72 hours, and then taken out, and the panel variations after 2 hoursand 24 hours were measured and summarized in Table 1 below. In Table 1below, the term flatness is a difference between a portion that is bentmost toward the upper polarizing plate and a portion that is bent mosttoward the lower polarizing plate in the liquid crystal panel, wherethis flatness can be confirmed using a known three-dimensional measuringinstrument (Dukin Co., Ltd.).

TABLE 1 Initial After 2 hours After 6 hours Flatness Flatness VariationFlatness Variation Example 1 2.2 2 −0.2 1.8 −0.4 Example 2 2.5 1.9 −0.61.6 −0.9 Example 3 1.7 1.6 −0.1 1.4 −0.3

1. A method for producing an optical film, comprising: subjecting apolymer film, on a surface of which an optical layer is formed, to aheat-treatment.
 2. The method for producing an optical film according toclaim 1, wherein the optical layer comprises a hard-coating layer, anantireflection layer, an antiglare layer or an antistatic layer.
 3. Themethod for producing an optical film according to claim 1, furthercomprising: treating the polymer film with steam, of which a temperatureis from 50° C. to 150° C., for from 10 seconds to 1 hour before theheat-treatment and forming the optical layer on the surface of thepolymer film after the steam treatment.
 4. The method for producing anoptical film according to claim 1, wherein a shrinkage force of thepolymer film before the heat-treatment along a first direction is from5.5N to 15N.
 5. The method for producing an optical film according toclaim 4, wherein a ratio (S1/S2) of the shrinkage force (S1) of thepolymer film before the heat-treatment along the first directionrelative to a shrinkage force (S2) of the polymer film before theheat-treatment along a second direction perpendicular to the firstdirection is 10 or more.
 6. The method for producing an optical filmaccording to claim 5, wherein the shrinkage force (S2) of the polymerfilm before the heat-treatment along a second direction perpendicular tothe first direction is from 0.01N to 2N.
 7. The method for producing anoptical film according to claim 4, wherein a ratio (SB/SA) of ashrinkage force (SB) of the polymer film before the heat-treatment alongthe first direction relative to a shrinkage force (SA) of the polymerfilm after the heat-treatment along the first direction is more than 1.8. The method for producing an optical film according to claim 1,wherein a shrinkage force of the polymer film after the heat-treatmentalong a first direction is from 5N to 10N.
 9. The method for producingan optical film according to claim 8, wherein a ratio (S1/S2) of theshrinkage force (S1) of the polymer film after the heat-treatment alongthe first direction relative to a shrinkage force (S2) of the polymerfilm after the heat-treatment along a second direction perpendicular tothe first direction is 13 or more.
 10. The method for producing anoptical film according to claim 1, wherein the heat-treatment isperformed at a temperature satisfying Equation 2 below.(Tg−60°)° C.≤T≤(Tg+50°)° C.  [Equation 2] wherein, Tg is a glasstransition temperature of the polymer film, T is a temperature of theheat-treatment, and each of units of the glass transition temperatureand the temperature of the heat-treatment is ° C.
 11. The method forproducing an optical film according to claim 1, wherein theheat-treatment is performed for from 10 seconds to 1,000 seconds.
 12. Amethod for producing a polarizing plate, comprising: attaching theoptical film produced by the method of claim 1 and a polarizing filmhaving a light absorption axis formed in one in-plane direction.
 13. Themethod for producing a polarizing plate according to claim 12, whereinthe optical film is attached to the polarizing film so that a ratio(S_(P)/S_(V)) of a shrinkage force (S_(P)) of the polarizing plate alongthe light absorption axis of the polarizing film relative to a shrinkageforce (S_(V)) of the polarizing plate along a direction perpendicular tothe light absorption axis direction is from 0.7 to 1.5.
 14. The methodfor producing a polarizing plate according to claim 12, wherein theoptical film is attached to the polarizing film so that a shrinkageforce of the polarizing plate along a direction parallel to the lightabsorption axis of the polarizing film is from 6.5N to 15N.
 15. Themethod for producing a polarizing plate according to claim 12, whereinthe optical film is attached to the polarizing film so that a shrinkageforce of the polarizing plate along a direction perpendicular to thelight absorption axis is from 6.0N to 15N.
 16. The method for producinga polarizing plate according to claim 12, wherein a shrinkage force ofthe optical film along a first direction of the polymer film is from 5Nto 10N and wherein the polarizing film and the optical film are attachedso that the first direction and the light absorption axis of thepolarizing film are perpendicular to each other.
 17. The method forproducing a polarizing plate according to claim 16, wherein a ratio(S1/S2) of a shrinkage force (S1) along a first direction of the polymerfilm relative to a shrinkage force (S2) along a second directionperpendicular to the first direction is 13 or more.
 18. The method forproducing a polarizing plate according to claim 12, wherein a shrinkageforce of the polarizing film along a direction parallel to the lightabsorption axis is from 0.1 to 15N.
 19. The method for producing apolarizing plate according to claim 12, wherein the smallest angle amongangles formed by one side of the polarizing film and the lightabsorption axis of the polarizing film is from 0 to 10 degrees or from80 to 100 degrees.
 20. The method for producing a polarizing plateaccording to claim 12, wherein the smallest angle among angles formed byone side of the polarizing film and the light absorption axis of thepolarizing film is from 35 to 55 degrees or from of 125 to 145 degrees.